Anisotropic conductive film and connected structure

ABSTRACT

Anisotropic conductive films, each including an insulating adhesive layer and conductive particles insulating adhesive layer in a lattice-like manner. Among center distances between an arbitrary conductive particle and conductive particles adjacent to the conductive particle, the shortest distance to the conductive particle is a first center distance; the next shortest distance is a second center distance. These center distances are 1.5 to 5 times the conductive particles&#39; diameter. The arbitrary conductive particle, conductive particle spaced apart from the conductive particle by the first center distance, conductive particle spaced apart from the conductive particle by first center distance or second center distance form an acute triangle. Regarding this acute triangle, an acute angle formed between a straight line orthogonal to a first array direction passing through the conductive particles and second array direction passing through conductive particles being 18 to 35°. These anisotropic conductive films have stable connection reliability in COG connection.

TECHNICAL FIELD

The present invention relates to an anisotropic conductive film, aconnecting method using the anisotropic conductive film, and a connectedstructure obtained by connection with the anisotropic conductive film.

BACKGROUND ART

Anisotropic conductive films are widely used when mounting electroniccomponents such as IC chips on substrates. In recent years, more highlydense wiring is demanded in compact electronic apparatuses such ascellular phones and notebook computers. As a measure for adaptinganisotropic conductive films to such highly dense wiring, there is knowna technology in which conductive particles are uniformly disposed in amatrix-like manner in an insulating adhesive layer of an anisotropicconductive film.

However, there is a problem in which even when conductive particles areuniformly arranged, connection resistance varies. This is becauseconductive particles placed on the edge of a terminal flow into spacesdue to melting of an insulating adhesive, and are therefore difficult tobe caught between terminals located below and above the particles. Toaddress this problem, there has been proposed that when a first arraydirection of conductive particles is a longitudinal direction of ananisotropic conductive film, a second array direction intersecting thefirst array direction is tilted at 5° or more and 15° or less withrespect to a direction orthogonal to the longitudinal direction of theanisotropic conductive film (Patent Literature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 4887700

SUMMARY OF INVENTION Technical Problem

However, as the bump size of an electronic component connected with theanisotropic conductive film becomes smaller, the number of conductiveparticles which can be trapped by the bump becomes smaller. Thus, theanisotropic conductive film described in Patent Literature 1 failed toprovide sufficient conduction reliability in some cases. Especially, ina so-called COG connection that connects a control IC of a liquidcrystal screen or the like to a transparent electrode on a glasssubstrate, the bump size becomes smaller due to the increased number ofterminals associated with higher definition liquid crystalline screenand the miniaturized IC chips. Consequently, it has become a challengeto increase the number of conductive particles that can be trapped by abump and enhance connection reliability.

To address this, an object of the present invention is to provide stableconnection reliability even when the anisotropic conductive film is usedin the COG connection.

Solution to Problem

The present inventor has found that when an anisotropic conductive filmincluding conductive particles arranged on an insulating adhesive layerin a lattice-like manner has a specific relationship between aninter-particle distance and an array direction of the conductiveparticles, anisotropic conductive connection can be performed withstable connection reliability even in COG connection in which highdensity wiring is required. Thus, the present invention has beencompleted.

That is, the present invention provides an anisotropic conductive filmincluding an insulating adhesive layer and conductive particles arrangedin the insulating adhesive layer in a lattice-like manner, wherein

when among center distances between an arbitrary conductive particle andconductive particles adjacent to the conductive particle, the shortestdistance to the arbitrary conductive particle is defined as a firstcenter distance, and the next shortest distance is defined as a secondcenter distance,

the first center distance and the second center distance are each 1.5 to5 times the particle diameter of the conductive particles, and

regarding an acute triangle formed by an arbitrary conductive particleP₀, a conductive particle P₁ spaced apart from the arbitrary conductiveparticle P₀ by the first center distance, and a conductive particle P₂spaced apart from the arbitrary conductive particle P₀ by the firstcenter distance or the second center distance, an acute angle α(hereinafter, also referred to as a tilt angle α in a second arraydirection) formed between a straight line orthogonal to a direction(hereinafter, referred to as a first array direction) of a straight linepassing through the conductive particles P₀ and P₁ and a direction(hereinafter, referred to as the second array direction) of a straightline passing through the conductive particles P₁ and P₂ is 18 to 35°.

The present invention further provides a method of connecting aconnection terminal of a first electronic component and a connectionterminal of a second electronic component with the above-describedanisotropic conductive film, wherein a longitudinal direction of theanisotropic conductive film is made coincident with a widthwisedirection of the connection terminal of the first electronic componentor the second electronic component, and in particular, a directionsubstantially orthogonal to the first array direction of the anisotropicconductive film is made coincident with a longitudinal direction of theconnection terminal of the first electronic component or the secondelectronic component.

Here, “substantially orthogonal” includes not only a direction strictlyorthogonal to the first array direction but also the range of adeviation caused when mounting an electronic component with theanisotropic conductive film. Usually, ±3° are included to the directionorthogonal to the first array direction.

In addition, the present invention provides a connected structure inwhich the first electronic component and the second electronic componentare connected through anisotropic conductive connection by theabove-described connecting method.

Advantageous Effects of Invention

According to the anisotropic conductive film of the present invention,the conductive particles are arranged at high density such that thefirst center distance as the shortest center distance and the secondcenter distance as the next shortest center distance among the centerdistances between the adjacent conductive particles are each 1.5 to 5times the particle diameter of the conductive particles. Furthermore,the conductive particles are arranged in the insulating adhesive layerin a lattice-like manner in specific directions. Consequently, aconnection for high density wiring can be performed while suppressing ashort circuit between adjacent terminals.

Furthermore, since the acute angle (tilt angle α in the second arraydirection) formed between the straight line orthogonal to the firstarray direction of the conductive particles and the second arraydirection is 18 to 35° in the anisotropic conductive film according tothe present invention, the number of conductive particles trapped in aconnection terminal can be increased by making anisotropic conductiveconnection while the direction substantially orthogonal to the firstarray direction of the anisotropic conductive film is made coincidentwith the longitudinal direction of the connection terminal. Thus, evenwhen the anisotropic conductive film according to the present inventionis used for COG connection, stable connection reliability can beobtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an arrangement diagram of conductive particles in ananisotropic conductive film of an example.

FIG. 2 is a diagram for explaining array directions of conductiveparticles in an anisotropic conductive film and a preferred orientationto a longitudinal direction of a connection terminal.

FIG. 3 is a diagram for explaining array directions of conductiveparticles in an anisotropic conductive film of another example and apreferred orientation to a longitudinal direction of a connectionterminal.

FIG. 4 is a diagram for explaining an arrangement of conductiveparticles in a connected product for evaluation including an anisotropicconductive film of an example.

FIG. 5 is a diagram illustrating a relationship between the number oftrapped particles per bump and frequency in connected products includinganisotropic conductive films according to an example and a comparativeexample.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail withreference to the drawings.

FIG. 1 is an arrangement diagram of conductive particles P in ananisotropic conductive film 1A according to an embodiment of the presentinvention. This anisotropic conductive film 1A includes an insulatingadhesive layer 10 and conductive particles P fixed to the insulatingadhesive layer 10 in a lattice-like arrangement.

In the anisotropic conductive film 1A, among center distances between anarbitrary conductive particle P₀ and conductive particles adjacent tothe conductive particle P₀, suppose a case where the shortest distanceis defined as a first center distance d1, and the next shortest distanceis defined as the second center distance d2. In this case, theconductive particle P₀, a conductive particle P₁ spaced apart from theconductive particle P₀ by a first center distance d1, and a conductiveparticle P₂ spaced apart from the conductive particle P₀ by a secondcenter distance form an acute triangle P₀P₁P₂. Regarding this acutetriangle P₀P₁P₂, the conductive particles are arrayed in a first arraydirection L1 passing through the conductive particles P₀ and P₁ at apitch d1; the conductive particles are also arrayed in a second arraydirection L2 passing through the conductive particles P₁ and P₂; andconductive particles are arrayed in a third array direction L3 passingthrough the conductive particles P₀ and P₂ at a pitch d2. Although thepitch d2 between the conductive particles in the third array directionis longer than the pitch d1 between the conductive particles in thefirst array direction L1 in this example, these pitches may be the same.

The particle diameter D of the conductive particles P is preferably 1 to10 μm from the viewpoint of prevention of a short circuit and stabilityof bonding between electrodes.

The first center distance d1 and the second center distance d2 are each1.5 to 5 times the particle diameter D of the conductive particles,preferably 1.8 to 4.5 times, and more preferably 2 to 4 times. When thefirst center distance d1 and the second center distance d2 areexcessively short, a connection between terminals with the anisotropicconductive film is likely to cause a short circuit. When the firstcenter distance d1 and the second center distance d2 are excessivelylong, the number of conductive particles trapped between terminalsbecomes insufficient.

The difference between the first center distance d1 and the secondcenter distance d2 is preferably less than 2 times the particle diameterD of the conductive particles P, more preferably less than 1.5 times,and further preferably the same or less than the particle diameter D.This is because an excessively large difference deteriorates bumptrapping properties during anisotropic conductive connection with theanisotropic conductive film 1A.

The density of the conductive particles P is preferably 2000 to 250000particles/mm². This particle density is appropriately adjusted dependingon the particle diameter and arrangement direction of the conductiveparticles P.

Even when attempting to manufacture the anisotropic conductive film inwhich conductive particles are arranged in a lattice-like manner at apredetermined density, the conductive particles may be sometimes lackedfrom the lattice position for reasons of practical manufacturingprocesses. Regarding the lacking of conductive particles from thelattice position, the number of continuously lacked conductive particlesP in this anisotropic conductive film 1A is preferably 6 or less, morepreferably 5 or less, and further preferably 4 or less, in each of thefirst array direction L1 and the second array direction L2, especiallyin each of the array directions L1, L2, and L3. Furthermore, when aregion of 10 particles continuous from a position where an arbitraryconductive particle is arranged in the first array direction and 10particles continuous from the position in the second array direction,that is, a region where 10 particles×10 particles (100 particles intotal) are arranged, is extracted, the number of conductive particlespresent in the region where 100 particles are to be arranged ispreferably 75 or more, more preferably 80 or more, further preferably 90or more, and particularly preferably 94 or more.

Such suppression of lacked conductive particles facilitates trapping ofthe conductive particles in a number sufficient for conduction by a bumpeven when any part of the anisotropic conductive film is used inconnecting a square bump with the anisotropic conductive film.Accordingly, the anisotropic conductive film can be adapted toanisotropic conductive connection at a fine pitch.

It is noted that as a method for suppressing lacking of the conductiveparticles in this manner, a wiping process is preferably repeatedlyperformed on a mold or a member having through holes when arranging theconductive particles P to the insulating adhesive layer 10 as describedlater.

In this anisotropic conductive film 1A, a tilt angle α in the secondarray direction is 18 to 35°. By defining the tilt angle α in the secondarray direction in this manner in the relationship between the particlediameter D and the pitches d1 and d2 as described above, the conductiveparticles for contributing to conduction can be ensured in a sufficientnumber in any part on the surface of the anisotropic conductive film 1Aadopted as a rectangular region used for anisotropic conductiveconnection of a rectangular connection terminal (bump) with thisanisotropic conductive film 1A.

In general, in anisotropic conductive connection on the production lineof electronic apparatuses, a connection terminal 3 and the anisotropicconductive film 1A are arranged such that the widthwise direction of theconnection terminal 3 is along the longitudinal direction of theanisotropic conductive film 1A. Therefore, from the viewpoint ofproductivity of anisotropic conductive films, it is preferred that, asillustrated in FIG. 2, a longitudinal direction Lt of the rectangularconnection terminal 3 is made coincident with a direction L0 orthogonalto the first array direction L1 (that is, the widthwise direction of theconnection terminal 3 is made coincident with the first array directionL1). In other words, it is desirable that the first array direction L1be substantially parallel to the longitudinal direction Lf of theanisotropic conductive film 1A, that is, it is desirable that the firstarray direction L1 of conductive particles be parallel to thelongitudinal direction Lf of the anisotropic conductive film 1A withinthe range of a variation in the arrangement of the conductive particles,which is caused during manufacture of the anisotropic conductive film.

On the other hand, from the viewpoint of improving properties oftrapping conductive particles in a connection terminal duringanisotropic conductive connection, it is preferred that all of the firstarray direction L1, the second array direction L2, and the third arraydirection L3 of conductive particles P be tilted with respect to thelongitudinal direction of an anisotropic conductive film 1B, asindicated by the anisotropic conductive film 1B illustrated in FIG. 3.It is especially preferred that an acute angle β (hereinafter, alsoreferred to as a tilt angle β) formed between the first array directionL1 and the longitudinal direction Lf of the anisotropic conductive film1B be 5 to 25°.

It is noted that this anisotropic conductive film 1B is configured in asimilar manner to the above-described anisotropic conductive film 1A,except that the first array direction L1 of the conductive particles Pis tilted with respect to the longitudinal direction Lf of theanisotropic conductive film 1B.

Here, in order to arrange conductive particles in a dense state so thatan anisotropic conductive film can be adapted to a connection of aterminal at a further finer pitch, as illustrated in FIG. 4 describedlater, the external tangent (double-dashed line) of a conductiveparticle P, which extends in the direction orthogonal to thelongitudinal direction Lf of the anisotropic conductive film 1B, maypass through conductive particles Pc and Pe adjacent to the conductiveparticle P. This can further increase the area of conductive particlesto the connection surface of the connection terminal 3, in a plandiagram in which the anisotropic conductive film 1B is superimposed onthe terminal surface of the connection terminal 3. This can prevent thenumber of conductive particles P, which are placed between theconnection terminals 3 facing each other during anisotropic conductiveconnection and pushed into the connection terminals 3 to allowconduction between the connection terminals 3, from becominginsufficient.

In the anisotropic conductive film according to the present invention,the structure of the conductive particles P themselves and the layerstructure or constituent resin of the insulating adhesive layer 10 maybe in various forms, as long as the conductive particles are arranged asdescribed above.

That is, as the conductive particles P, any of conductive particles usedin a known anisotropic conductive film can be appropriately selected andused. Examples of the conductive particles P may include metal particlessuch as nickel, cobalt, silver, copper, gold and palladium or metalcoated resin particles. Two or more of these can be used in combination.

As the insulating adhesive layer 10, any insulating resin layer used ina known anisotropic conductive film can be appropriately adopted.Examples of the insulating adhesive layer 10 to be used may include aphoto-radical polymerization-type resin layer containing an acrylatecompound and a photo-radical polymerization initiator, a thermal radicalpolymerization-type resin layer containing an acrylate compound and athermal radical polymerization initiator, a thermal cationicpolymerization-type resin layer containing an epoxy compound and athermal cationic polymerization initiator, and a thermal anionicpolymerization-type resin layer containing an epoxy compound and athermal anionic polymerization initiator. Each of these resin layers canbe polymerized as necessary. The insulating adhesive layer 10 mayinclude a plurality of resin layers.

The insulating adhesive layer 10 may further include, as necessary, aninsulating filler such as silica fine particles, alumina, and aluminumhydroxide. The amount of the insulating filler to be added is preferably3 to 40 parts by mass with respect to 100 parts by mass of the resin forforming the insulating adhesive layer. This can inhibit the conductiveparticles P from unnecessarily moving due to melted resin even when theinsulating adhesive layer 10 is melted during anisotropic conductiveconnection.

A method of fixing the conductive particles P to the insulating adhesivelayer 10 into the above-described arrangement may include: preparing amold with concaves corresponding to the arrangement of the conductiveparticles P by a known method such as machining, laser beam machining,and photolithography; pouring conductive particles into the mold;filling an insulating adhesive layer-forming composition on the pouredconductive particles; curing the composition in the mold; and releasinga product from the mold. Using this mold, a further mold may be preparedwith a material having low rigidity.

Another example of the method may include: disposing, on an insulatingadhesive layer-forming composition layer, a member with through holesarranged in a predetermined manner in order to place the conductiveparticles P in the above-described arrangement on the insulatingadhesive layer 10; and supplying the conductive particles P on themember to allow the conductive particles P to pass through the throughholes.

When performing anisotropic conductive connection between a connectionterminal of a first electronic component such as a flexible substrate ora glass substrate and a connection terminal of a second electroniccomponent such as an IC chip or an IC module with the anisotropicconductive film 1A or 1B according to the present invention, thelongitudinal direction Lf of the anisotropic conductive film 1A or 1B ismade coincident with the widthwise direction of the connection terminal3 of the first electronic component or the second electronic component,as illustrated in FIG. 2 and FIG. 3. Accordingly, the number of trappedconductive particles P in the connection terminals can be sufficientlyincreased by taking advantage of the arrangement of the conductiveparticles P in the anisotropic conductive film 1A or 1B according to thepresent invention. Especially, the use of the anisotropic conductivefilm 1B in which all of the array directions of the conductive particlesP are tilted with respect to the longitudinal direction Lf of theanisotropic conductive film can significantly enhance the properties oftrapping the conductive particles P in the connection terminal 3.

For example, when performing COG connection for high density wiring byusing a glass substrate or the like having a connection terminal formedfrom a transparent electrode as the first electronic component and an ICchip or the like as the second electronic component, more specifically,when the size of the connection surface of these connection terminals is8 to 60 μm in width and 400 μm or less in length (the lower limit is thesame as the width), or when the width in the widthwise direction of theconnection surface of the connection terminals is less than 7 times theparticle diameter of the conductive particles, the number of conductiveparticles that can be trapped in the connection terminals particularlyincreases in a stable manner when compared with the known anisotropicconductive connection, thereby enabling enhancement of connectionreliability. It is noted that when the width in the widthwise directionof the connection terminal surface is smaller than this defined size,connection failures are often caused. When it is larger than thisdefined size, it becomes difficult to be adapted to high densitymounting required in COG connection. Furthermore, when the length of theconnection terminal surface is shorter than this defined size, stableconduction becomes difficult to obtain. When it is longer than thisdefined size, biased contact may be caused. On the other hand, theminimum distance between the connection terminals is determinedaccording to the width in the widthwise direction of the connectionsurface of the connection terminals, and may be, for example, 8 to 30μm.

In fine pitch terminals that can be connected to each other with theanisotropic conductive film according to the present invention, theminimum distance between the terminals spaced from and adjacent to eachother in the parallel direction of terminals including the terminalsconnected to and facing each other may be less than 4 times theconductive particle diameter. Here, the minimum distance may bemisaligned in the parallel direction within the range that enablesanisotropic connection. In this case, the width in the widthwisedirection of the connection surface of the terminals to be connected toeach other may be less than 7 times the particle diameter of theconductive particles.

The present invention also encompasses a connected structure obtained bysuch anisotropic conductive connection between the first electroniccomponent and the second electronic component.

EXAMPLES

Hereinafter, the present invention will be specifically described on thebasis of examples.

Test Example 1

Conductive particles P (particle diameter D=4 μm) were arranged in ananisotropic conductive film under a condition of first center distanced1=second center distance d2=10 μm, and a tilt angle α was varied asshown in Table 1. In such a case, the maximum number of particles andthe minimum number of particles of the conductive particles that couldbe trapped by a bump before heating and pressurization were calculatedby superimposing a narrow bump having an electrode size of 15 μm×100 μmon a pattern of the anisotropic conductive film. In this case, thelongitudinal direction of the anisotropic conductive film was madecoincident with the widthwise direction of the bump. Furthermore, when50% or more of the area of a particle was outside the edge portion ofthe bump, the particle was not counted as the conductive particle thatcould be trapped by the bump.

From this result, a tendency of the tilt angle α and particle trappingproperties of the bump can be observed. The result is shown in Table 1.

TABLE 1 Tilt angle α (°) 0° 5° 15° 18° 20° 25° 30° 35° 40° 45° Maximum20 13 13 14 14 14 18 18 13 14 number of particles Minimum 9 9 9 11 11 1212 12 7 7 number of particles

As understood from Table 1, when the tilt angle α is 18 to 35°, thedifference between the minimum number of particles and the maximumnumber of particles trapped by the bump is small and stable. Thus, suchan angle is effective for a narrow bump.

In contrast to this, an excessively small tilt angle α causes thedifference in the number of trapped particles to increase. This isbecause an excessively small tilt angle causes the occupation degree ofa particle array on the edge of a bump to directly influence the numberof trapped particles. When the tilt angle α is excessively large, asimilar phenomenon is also caused, and there is a tendency that thenumber of particles lying outside a bump increases.

As understood from the above, the tilt angle α needs to be appropriatelymaintained so that a narrow bump has constant trapping efficiency formaintaining stable conductivity.

Examples 1 to 8 and Comparative Examples 1 to 5

Next, in order to specifically examine a relationship between thedistance between particles and the tilt angle α of conductive particles,anisotropic conductive films in which conductive particles (SekisuiChemical Co., Ltd., AUL704, particle diameter: 4 μm) were arranged asshown in Table 2 were manufactured using resins shown in Table 2 in thefollowing manner. That is, a mixed solution of insulating resinscontaining a thermoplastic resin, a thermosetting resin, and a latentcuring agent in the composition shown in Table 2 was prepared. The mixedsolution was applied onto a PET film with a film thickness of 50 μm, anddried in an oven at 80° C. for 5 minutes. Thus, an adhesive layer with athickness of 20 μm was formed on the PET film.

On the other hand, a mold having the array pattern of convex portionscorresponding to the arrangement shown in Table 2 was prepared. Then, apellet of known transparent resin in a melted state was poured into themold, and cooled to be solidified. Thus, a resin mold having convexportions corresponding to the arrangement pattern shown in Table 2 wasformed. Conductive particles were filled in the concave portions of thisresin mold, and covered with the above-described adhesive layer ofinsulating resin. The thermosetting resin contained in the insulatingresin was cured by ultraviolet curing. Then, the insulating resin waspeeled from the mold. In this manner, an anisotropic conductive filmaccording to each of the examples and comparative examples wasmanufactured.

Examples 9 to 13 and Comparative Examples 6 and 7

Anisotropic conductive films according to Examples 9 to 13 andComparative Examples 6 and 7 were manufactured in the similar manner tothe above-described examples and comparative examples, except that theconductive particles were arranged as shown in Table 3.

Here, Comparative Example 7 has a shape of a tetragonal lattice, andExamples 3 and 9 to 13 each have a shape of hexagonal lattice.

In Comparative Example 1 and Comparative Example 6, the conductiveparticles were dispersed in a low boiling point solvent, and theobtained liquid was sprayed so that the conductive particles wererandomly arranged on the same plane.

The center distance d (the first center distance d1 and the secondcenter distance d2) between adjacent conductive particles of theconductive particles was measured using an optical microscope. In thiscase, 100 particles or 50 pairs of particles present in the first arraydirection or the second array direction were arbitrarily measured, andan average value thereof was calculated. Thus, it was confirmed that thecalculated value was a desired center distance d between adjacentparticles. The results are shown in Table 2.

On the other hand, in Comparative Examples 1 and 6, 100 conductiveparticles were arbitrarily selected, and the center distance betweenparticles closest to each other of the conductive particles wasmeasured.

Evaluation

The anisotropic conductive film according to each of the examples andcomparative examples was evaluated for (a) the number of trappedparticles, (b) initial conduction resistance, (c) conductionreliability, and (d) short circuit incidence, in the following methods.The results are shown in Table 2 and Table 3.

(a) The Number of Trapped Particles

(a-1) Average Number

With the anisotropic conductive film according to each of the examplesand comparative examples, 100 bumps of 15×100 μm and a glass substratewere heated and pressurized (180° C., 80 MPa, 5 seconds) to obtain aconnected product. In this case, the longitudinal direction of theanisotropic conductive film was made coincident with the widthwisedirection of the bumps. Then, the number of trapped particles in eachbump was measured, and the average number of trapped particles per bumpwas calculated.

(a-2) Minimum Number

Of the numbers of trapped particles in the bumps measured in (a-1), theminimum number of trapped particles was obtained.

(b) Initial Conduction Resistance

The anisotropic conductive film according to each of the examples andcomparative examples was placed between a glass substrate and an IC forevaluation of initial conduction and conduction reliability, and heatedand pressurized (180° C., 80 MPa, 5 seconds) to obtain a connectedproduct for evaluation. In this case, the longitudinal direction of theanisotropic conductive film was made coincident with the widthwisedirection of the bump. Then, the conduction resistance of the connectedproduct for evaluation was measured.

Here, the terminal patterns of the IC for evaluation and the glasssubstrate corresponded to each other, and the sizes thereof are asfollows.

IC for Evaluation of Initial Conduction and Conduction Reliability

Outer diameter: 0.7×20 mm

Thickness: 0.2 mm

Bump specifications: gold plating, height 12 μm, size 15×100 μm,distance between bumps 15 μm

Glass Substrate

Glass material: manufactured by Corning Incorporated

Outer diameter: 30×50 mm

Thickness: 0.5 mm

Electrode: ITO wiring

(c) Conduction Reliability

The connected product for evaluation between the IC for evaluation andthe anisotropic conductive film according to each of the examples andcomparative examples prepared in (b) was placed in a constanttemperature bath at a temperature of 85° C. and a humidity of 85% RH for500 hours, and thereafter the conduction resistance was measured in thesimilar manner to that in (b). It is noted that the conductionresistance of 5Ω or more is not preferred from the viewpoint ofpractical conduction stability of the connected electronic component.

(d) Short Circuit Incidence

As an IC for evaluation of short circuit incidence, the following IC(7.5 μm spaced comb teeth TEG (test element group)) was prepared.

Outer diameter: 1.5×13 mm

Thickness: 0.5 mm

Bump specifications: gold plating, height 15 μm, size 25×140 μm,distance between bumps 7.5 μm

The anisotropic conductive film according to each of the examples andcomparative examples was placed between an IC for evaluation of shortcircuit incidence and a glass substrate having a pattern correspondingto the IC for evaluation, and heated and pressurized under a connectioncondition similar to those in (b) to thereby obtain a connected product.The short circuit incidence of the connected product was calculated. Theshort circuit incidence is calculated according to “the number of shortcircuits/the total number of 7.5 μm spaces”. The short circuit incidenceof 1 ppm or more is not preferred from the viewpoint of practicalmanufacture of the connected structure.

TABLE 2 Comparative Comparative Comparative Comparative Example ExampleExample 1 Example 2 Example 3 Example 4 1 2 Insulating resin Phenoxyresin *1 60 60 60 60 60 60 Epoxy resin *2 40 40 40 40 40 40 Cationiccuring agent *3 2 2 2 2 2 2 Arrangement of conductive particles Particlediameter D (μm) 4 4 4 4 4 4 Tilt angle α (°) Random 0 5 15 18 20 Centerdistance between Ave 10 12 12 12 12 12 adjacent particles Min 4  (d = d1= d2) (μm) Ratio between inter-particle 2 2 2 2 2 distance and particlediameter: (d-D)/D Evaluation Number of trapped particles 9.6 3.6 5.5 5.57 7.9 (Average) Number of trapped particles 5 0 2.3 2.7 4.7 6.2(minimum) Initial conduction resistance 0.2 0.2 0.2 0.2 0.2 0.2 (Ω)Conduction reliability (Ω) Less than 5 5 or more 5 or more 5 or moreLess Less than 5 than 5 Short circuit incidence (ppm) 3000 Less than 1Less than 1 Less than 1 Less Less than 1 than 1 Example ExampleComparative Example Example Example Example 3 4 Example 5 5 6 7 8Insulating resin Phenoxy resin *1 60 60 60 60 60 60 60 Epoxy resin *2 4040 40 40 40 40 40 Cationic curing agent *3 2 2 2 2 2 2 2 Arrangement ofconductive particles Particle diameter D (μm) 4 4 4 4 4 4 4 Tilt angle α(°) 30 35 45 35 35 18 18 Center distance between 12 12 12 6 20 6 20adjacent particles (d = d1 = d2) (μm) Ratio between inter-particle 2 2 20.5 4 0.5 4 distance and particle diameter: (d-D)/D Evaluation Number oftrapped particles 8.2 8.2 4.8 34.7 5.5 33.6 5.4 (Average) Number oftrapped particles 7 6.5 2.7 31.4 4 31 3.6 (minimum) Initial conduction0.2 0.2 0.2 0.2 0.2 1.2 0.2 resistance (Ω) Conduction reliability (Ω)Less Less 5 or more Less Less Less Less than 5 than 5 than 5 than 5 than5 than 5 Short circuit incidence (ppm) Less Less Less than 1 Less LessLess Less than 1 than 1 than 1 than 1 than 1 than 1 (Note) *1 NipponSteel & Sumitomo Metal Corporation, YP-50 (thermoplastic resin) *2Mitsubishi Chemical Corporation, jER 828 (thermosetting resin) *3Sanshin Chemical Industry Co., Ltd., SI-60L (latent curing agent)

TABLE 3 Comparative Comparative Example Example Example Example ExampleExample 6 Example 7 9 10 11 12 13 Insulating resin Phenoxy resin *1 6060 60 60 60 60 60 Epoxy resin *2 40 40 40 40 40 40 40 Cationic curingagent *3 2 2 2 2 2 2 2 Arrangement of conductive particles Particlediameter D (μm) 4 4 4 4 4 4 4 Arrangement density (particles/mm²) 1000010000 10000 10000 10000 10000 10000 Tilt angle α (°) Random 90 30 30 3030 30 Tilt angle β (°) — 15 5 10 15 20 25 Center distance betweenadjacent particles Ave 10 10 10 10 10 10 10 (d = d1 = d2) (μm) Min 4 Ratio between inter-particle distance and — 1.5 1.5 1.5 1.5 1.5 1.5particle diameter: (d-D)/D Evaluation Number of trapped particles(Average) 8 12 14 14 14 14 14 Number of trapped particles (minimum) 0 410 11 12 11 10 Initial conduction resistance (Ω) 0.2 0.2 0.2 0.2 0.2 0.20.2 Conduction reliability (Ω) Less than 5 Less than 5 Less Less LessLess Less than 5 than 5 than 5 than 5 than 5 Short circuit incidence(ppm) 3000 100 Less Less Less Less Less than 1 than 1 than 1 than 1 than1 (Note) *1 Nippon Steel & Sumitomo Metal Corporation, YP-50(thermoplastic resin) *2 Mitsubishi Chemical Corporation, jER 828(thermosetting resin) *3 Sanshin Chemical Industry Co., Ltd., SI-60L(latent curing agent)

As understood from Table 2, when the tilt angle α of conductiveparticles is 18 to 35°, reduced initial conduction resistance, highconduction reliability, and suppressed short circuit incidence areachieved, and anisotropic conductive connection adapted to high densitywiring having a terminal width of about 4 times the particle diametercan be performed.

In contrast to this, it is understood that in Comparative Example 1, anexcessively high particle density leads to worsened insulation.Furthermore, in Comparative Example 2 to Comparative Example 5, the tiltangle α is outside the range of 18 to 35°, the number of trappedparticles is low, and conduction reliability is lacked.

Furthermore, as understood from Table 3, in Examples 9 to 13 in whicheach array direction of conductive particles is tilted to thelongitudinal direction of the anisotropic conductive film, excellentconduction reliability and reduced short circuit incidence are similarlyachieved. A connected product for evaluation obtained by connecting aglass substrate and an IC for evaluation of initial conduction andconduction reliability with the anisotropic conductive film according toeach of Examples 9 to 13 was observed. As a result, as apparent in thearrangement of conductive particles illustrated in FIG. 4, an externaltangent (double-dashed line) of a conductive particle P in alongitudinal direction Lt of a bump 3 overlapped conductive particles Pcand Pe adjacent to the conductive particle P, and the external tangentpassed through the conductive particles Pc and Pe. This demonstratesthat even when the width of the bump 3 becomes further narrower,conductive particles in a number sufficient for conduction can betrapped.

In comparison between the appearances of the connected products forevaluation including the anisotropic conductive films according toComparative Example 7 and Examples 9 to 13, a difference in a dent statebetween the conductive particle Pc located in a center portion in thewidth direction of the bump 3 and the conductive particle Pe located onthe edge of the bump 3 was smaller in the connected products forevaluation including the anisotropic conductive films according toExamples 9 to 13 than in the connected product for evaluation includingthe anisotropic conductive film according to Comparative Example 7. Thisdemonstrates that the use of the anisotropic conductive films accordingto the examples enables achievement of more uniform pressure bonding. Itis noted that when the bump area is narrow, conductive particles are notnecessarily trapped both on the edge and in the center portion in thewidth direction of one bump 3. Therefore, the above-described resultswere obtained by observing the conductive particle trapped on the edgeand the conductive particle trapped in the center portion in the widthdirection in any one of many bumps arranged in parallel.

Examples 14 to 19

In Examples 3 and 9 to 13, the particle diameter D of conductiveparticles was changed from 4 μm to 3 μm, the center distance betweenadjacent particles was defined as 6 μm (that is, (d−D)/D=1), and thearrangement density was defined as 28000 particles/mm². With theconditions, anisotropic conductive films of Examples 14 to 19 weremanufactured, and evaluated in a similar manner. As a result, these alsoachieved low initial conduction resistance, high conduction reliability,and short circuit incidence suppressing effects, which weresubstantially similar to those in Examples 3 and 9 to 13. Furthermore,in connected products for evaluation of these, the dent states of theconductive particle located on the edge of the bump and the conductiveparticle located in the center portion in the width direction were alsosimilar to those in Examples 9 to 13.

Furthermore, anisotropic conductive films having a particle density of60000 particles/mm² prepared in Example 14 and Comparative Example 1were each connected with an IC including a bump having a bump area of700 μm² (bump size: 14 μm×50 μm, distance between bumps: 14 μm), in asimilar manner to when the number of trapped particles was measured inExample 1. Then, the frequency of trapping of conductive particles inone bump was studied. The results are shown in FIG. 5.

As understood from FIG. 5, in Example 14, the incidence abruptlyincreases when the number of trapped particles per bump is around 9,compared to Comparative Example 1, and the number of trapped conductiveparticles per bump is stabilized.

Examples 20 to 25

In Examples 3 and 9 to 13, the particle diameter D of conductiveparticles was not changed but still 4 μm, the center distance betweenadjacent particles was defined as 7 μm (that is, (d−D)/D=0.75, and thearrangement density: 20000 particles/mm²). With the conditions,anisotropic conductive films according to Examples 20 to 25 weremanufactured, and evaluated in a similar manner. As a result, these alsoachieved low initial conduction resistance, high conduction reliability,and short circuit incidence suppressing effects, which weresubstantially similar to those in Examples 3 and 9 to 13. Furthermore,in connected products for evaluation of these, the dent states of theconductive particle located on the edge of the bump and the conductiveparticle located in the center portion in the width direction were alsosimilar to those in Examples 9 to 13.

Examples 26 to 31

In Examples 3 and 9 to 13, the particle diameter D of conductiveparticles was not changed but still 4 μm, the center distance betweenadjacent particles was defined as 16 μm (that is, (d−D)/D=3, and thearrangement density: 4000 particles/mm²). With the conditions,anisotropic conductive films according to Examples 26 to 31 weremanufactured, and evaluated in a similar manner. As a result, theseshowed initial conduction resistance higher than those in Examples 3 and9 to 13, but there was no practical problem. The high conductionreliability and short circuit incidence suppressing effects weresubstantially similar to those in Examples 3 and 9 to 13. It isconsidered that this may be because the anisotropic conductive filmsaccording to Examples 26 to 31 had low arrangement density of theconductive particles. Furthermore, in connected products for evaluationof these, the dent states of the conductive particle located on the edgeof the bump and the conductive particle located in the center portion inthe width direction were also similar to those in Examples 9 to 13.

Examples 32 to 33

To 100 parts by mass of insulating resins, 20 parts by mass of a silicafine particle filler (silica fine particle, AEROSIL RY200, NipponAerosil Co., Ltd.) were added in Examples 5 and 7. With the conditions,anisotropic conductive films were manufactured in a similar manner toExamples 5 and 7, and evaluated. As a result, there were obtained lowinitial conduction resistance, high conduction reliability, and shortcircuit incidence suppressing effects, which were similar to those inExamples 5 and 7.

REFERENCE SIGNS LIST

-   -   1A, 1B anisotropic conductive film    -   connection terminal or bump    -   10 insulating adhesive layer    -   L0 direction orthogonal to first array direction    -   L1 first array direction    -   L2 second array direction    -   L3 third array direction    -   Lf longitudinal direction of anisotropic conductive film    -   Lt longitudinal direction of connection terminal    -   d1 first center distance, pitch    -   d2 second center distance, pitch    -   D particle diameter of conductive particle    -   P, P₀, P₁, P₂, Pc, Pe conductive particle    -   α tilt angle    -   β tilt angle

1. An anisotropic conductive film comprising an insulating adhesivelayer and conductive particles arranged in the insulating adhesive layerin a lattice-like manner, wherein when among center distances between anarbitrary conductive particle and conductive particles adjacent to theconductive particle, a shortest distance to the arbitrary conductiveparticle is defined as a first center distance, and a next shortestdistance is defined as a second center distance, the first centerdistance and the second center distance are each 1.5 to 5 times aparticle diameter of the conductive particles, and regarding an acutetriangle formed by an arbitrary conductive particle P₀, a conductiveparticle P₁ spaced apart from the arbitrary conductive particle P₀ bythe first center distance, and a conductive particle P₂ spaced apartfrom the arbitrary conductive particle P₀ by the first center distanceor the second center distance, an acute angle α formed between astraight line orthogonal to a direction (hereinafter, referred to as afirst array direction) of a straight line passing through the conductiveparticles P₀ and P₁ and a direction (hereinafter, referred to as asecond array direction) of a straight line passing through theconductive particles P₁ and P₂ is 18 to 35°.
 2. The anisotropicconductive film according to claim 1, wherein a difference between thefirst center distance and the second center distance is less than 2times the particle diameter of the conductive particles.
 3. Theanisotropic conductive film according to claim 1, wherein the firstarray direction is substantially parallel to a longitudinal direction ofthe anisotropic conductive film.
 4. The anisotropic conductive filmaccording to claim 1, wherein, when a direction passing through theconductive particles P₀ and P₂ is defined as a third array direction,the first array direction, the second array direction, and the thirdarray direction are tilted with respect to the longitudinal direction ofthe anisotropic conductive film.
 5. The anisotropic conductive filmaccording to claim 4, wherein an angle β formed between the first arraydirection and the longitudinal direction of the anisotropic conductivefilm is 5 to 25°.
 6. The anisotropic conductive film according to claim1, wherein a density of the conductive particles is 2000 to 250000particles/mm2.
 7. The anisotropic conductive film according to claim 1,wherein a number of continuously lacked conductive particles is 6 orless in each of the first array direction and the second arraydirection.
 8. A connecting method of connecting a connection terminal ofa first electronic component and a connection terminal of a secondelectronic component with the anisotropic conductive film according toclaim 1, wherein a longitudinal direction of a connection terminal ofthe anisotropic conductive film is made coincident with a widthwisedirection of the connection terminal of the first electronic componentor the second electronic component.
 9. The connecting method accordingto claim 8, wherein a direction substantially orthogonal to the firstarray direction of the anisotropic conductive film is made coincidentwith a longitudinal direction of the connection terminal of the firstelectronic component or the second electronic component.
 10. Theconnecting method according to claim 8, wherein the first electroniccomponent is a glass substrate having a connection terminal formed froma transparent electrode, and the second electronic component is an ICchip.
 11. The connecting method according to claim 8, wherein a size ofa connection surface of the connection terminal is 8 to 60 μm in widthand 400 μm or less in length.
 12. A connected structure in which a firstelectronic component and a second electronic component are connectedthrough anisotropic conductive connection by the connecting methodaccording to claim 8.